Electric discharge device and seal therefor



Sept. 26, 1939. T. A. ELDER Er AL ELECTRIC DISCHARGE DEVICE AND SEAL THEREFOR Original Filed Oct. 4, 1934 Inventors: Thomas A. Elder, Albert C Gable,

by The Attorney rl i l lafqisfl n gli Famed sept. 26,1939

PATENT OFFICE ELECTRIC DISCHARGE DEVICE AND SEAL THEREFOR Thomas A. Elder and Albert C. Gable, Scotia,

N. Y., assignors to General Electric Company, a corporation oi' New York Original application October 4, 1934, Serial No.

146,808. Divided and this application November 15, 1938, Serial No. 240,569

4 Claims.

'I'he present invention relates to electron discharge apparatus, and more particularly to the glass to metal seals employed in thermionic devices of the metal type. 'Ihis application is a division of Serial No. 746,808, filed October 4, 1934 in the names of Thomas A. Elder and Albert C. Gable and subsequently converted into a sole application in the name of Thomas A. Elder.

When metal instead of glass is employed for envelope material of the space current or other form of electrical discharge device, one of the problems encountered is that of passing the leading-in conductors through the metal envelope in an insulating manner. This problem is particularly diilicult in case the electric discharge device is of the power type which not only necessitates fairly high voltage between the various leadingin conductors, hence calling for considerable insulation therebetween, but in addition, requires conductors of considerable current-carrying capacity, i. e., of relatively large diameter.

In the application Serial No. 746,808 above re- Y ferred to, there is described and claimed-an improved type of seal wherein the leading-in conductors are respectively supported by means of glass fused within cylinders or eyelets which consist of nickel-iron-cobalt alloy. It is one object of the present invention to provide means whereby seals of this general character may be formed independently of the discharge device as a whole and thereafter separately appended to the device.

In this connection it is found that some difilculty is encountered with respect to breaking of the glass component of the seal when the eyelet is joined to the discharge envelope by means of a fused metal joint. 'Ihis difficulty is avoided in accordance with the present invention by spacing the glass from that end of the eyelet which is to be used as the joining part. The claims appended hereto are to be understood as being mainly directed to this feature.

Other objects and features of the invention will be apparent as the speciiication is perused in connection with the accompanying drawing in which Fig. 1 shows an elevational view, partly in section, of a tube containing several of the improved seals and electrode supports; Figs, 2, 3, and 4 are sectional views of modiiied forms of seals.

Referring more particularly to Fig. l, which illustrates only one of the many types of allmetal tubes in which the improved seals may be employed to advantage, numeral I designates a cylinder consisting of any readily workable, inexpensive metal, such as iron, nickel, etc., which is closed at the top (as shown) by a metal header member 2 and at the bottom by a metal header member 3. The member 3 may be fabricated of the same metal as cylinder I, but the header 2 is (Cl. Z50-27.5)

constituted of a special alloy suitable for sealing to glass without strain, as will be explained presently. The header members are both provided with anges which fit snugly within the cylinder and may be secured thereto, as by welding.

The interior assembly of the tube is illustratively exemplied as taking the form of a 4-electrode device having a cathode 4, an electrostatic control grid 5, a pair of screen grids 6, and an anode 1. The cathode is preferably of the indirectly heated type and is constituted of a cylinder containing a heater (not shown) which is extended through the bottom of the cathode and connects with a leading-in conductor 8. The cathode itself is conveniently supported from the header 3 by a pair of uprights 9 which t snugly within metal collars I secured respectively to the cathodeand the header.

The control member 5 conveniently takes the form of a sheet metal disc, circular in shape, made of foraminated material and mounted in a manner described hereinafter, transverse to the longitudinal axis of the tube. The screen grids 6, also provided with perforations, are mounted on both sides of the control member 5 and conveniently take the form of dish-shaped members which are anged and fit snugly within the envelope, resting on one another.

The anode is constituted of a cylindrical member terminating at the end nearer the control member in a thick wall in which a heavy support rod I I of copper and other suitable metal may be screwed. The other end of the anode terminates in a fiange which curves inwardly, taking the form roughly of a circular section in order to eliminate or reduce the possibility of sharp edges.

Surrounding the support rod II there is a metal cylinder I2, the lower end of which terminates in a curved portion, similar to that provided on the anode, and the upper end has an outwardly extending flange which is secured, as by welding, to the upper header member.

The anode support rod II is insulatingly supported from the header member 2 by means of a seal improved in accordance with the present invention. For this purpose, the header 2 is rst provided with an opening at the center, through which the rod passes, this opening being contained within a, curved portion of the header member, indicated by reference character I3. It is apparent that instead of forming the portion I3 integral with the header 2, such portion may be made as a separate member and welded or otherwise secured to the header. A cylinder I4 of glass provided with transverse corrugations in order to increase the insulation distance, is sealed at the lower end to the curved portion I3 of the header member and at the upper end is sealed to a metal cap I5. The support rod II is welded or otherwise secured to the cap member and obviously in view of the rigid joint between the cap member, the glass cylinder and the header, which in turn is secured to the container I, the support rod- II and the anode are rigidly mounted within the envelope. Electrical connection may be made to the anode 1 through the support rod II by means of a rod I6 which is welded or otherwise secured to the cap member I5 on the opposite side thereof from the support rod II.

For bringing out the various leading-in conductors through the lower metal header 3, specially designed seals are employed in accordance with the present invention. The seals shown by way of example in the tube assembly of Fig. 1 involve the use of an eyelet member I1 provided at one end with an outwardly extending ange in order to be secured, either to the underside or the upper side of the header member. There is a globule, bead, or cylinder I 8 of glass or other vitreous material within the eyelet which may support and insulate any one of the leading-in conductors or support rods from the eyelet, and hence from the header member. A hermetic seal is formed between the conductor, the glass and the eyelet, preferably by means of a gas flame which is directed at the proper position on the eyelet after the conductor and glass members have been assembled in the eyelet. The seal, including the conductor, glass, and eyelet is completed as a unit apart from the header member, after which the eyelet is secured, as by welding to the header.

It will be noted that the length of the glass member I8 is considerably less than the length of the eyelet I1. In order to reduce any tendency for the seal to be deleteriously affected by the heat generated at the weld, it is desirable to position the glass member within the eyelet as far as possible from the flanged portion of the eyelet Where the weld to the header member is made. A substantial space may also be left between the other end of the eyelet and the glass mass. The position of the glass member within the eyelet may be predetermined by suitable and well-known xtures and jigs on which'the members to be sealed are assembled and heated by the gas ilame referred to hereinbefore.

In order to ensure a vacuum-tight seal under all manufacturing and operating conditions between the glass I8, the eyelet I1 and the leadingin conductor, these members should preferably have substantially the same thermal expansion characteristic over the entire temperature range between C. and the softening temperatureof the glass. An example of glass and metal which may be satisfactorily sealed under these conditions has been disclosed and claimed in the Burger and Hull Patent No. 2,071,196, granted February 16, 1937, and assigned to the same assignee as the present invention. The glass may consist of approximately 65% silica (S102), 23% boric oxide (B203), 7% sodium oxide (NazO) and 5% aluminum oxide (A1203) sealed in a strain-free manner to an alloy of 18% cobalt (Co) 28% nickel (Ni) and 54% iron (Fe).

In securing the eyelet member I1 to the header member, it is first necessary to provide openings in the header through which the various leadingin conductors pass, and the flanged portion of each eyelet is then secured as by welding about each of these openings.

The conductor which passes through the glass portion contained in the metal eyelet may also constitute a support member for the electrode t0 which itis connected. Such a structure has been shown in Fig. 1 in which the combined support member and leading-in conductor I9 pass through the header member 3 and the lower screen grid 6 in an insulating manner to support the control grid in position. Surrounding the rod or support member I9, there is an insulating sleeve 20 contained within a metal tube 2l which carries a flange at each end in order to be welded to the underside of the lower screen grid and the upperside of the header 3. In addition to 'being supported by the rod I9, the control grid is also spaced from the lower screen grid by means of several equidistantly positioned spacer members 22, constituted of a block of glass, quartz or other refractory insulating material into which rigid wires 23 are sealed at one end and secured at the other end to the electrodes 5 and 5. It is therefore apparent that the control electrode 5 is rigidly and accurately mounted within the space contained between the screen grids 5 and yet proper provision has been made for insulatingly bringing out a leading-in conductor from the control grid to the exterior of the tube.

For evacuation purposes there is provided a metal tubulation 24 which is secured to the lower header and communicates through a large opening in the lower screen grid 5 with the upper interior of the tube. A pump may be attached to the lower end of the tubulation 25 and when the evacuation is complete and gas or a source of vapor introduced, if desired, the tubulation is collapsed and welded as is disclosed and claimed in the H. J. Nolte Patent No. 2,124,428, granted July 19, 1938, and assigned to the same assignee as the present invention.

The primary purpose of the screen grids 8 is to intercept the electrostatic lines of force which originate at the anode or the cathode and which normally would extend as far as the control member, causing deleterious currents to flow between the electrodes and thus affect the control normally exercised by the grid 5.

Instead of employing the eyelet form of seal for carrying the conductors 8 and I9 through the lower header member, it may be desirable to use any one of the seal constructions shown in Figs. 2, 3 and 4. In Fig. 2, reference character 30 refers to a portion of a metal container which may, for example, comprise either of the header members 2, 3cr the container I illustrated in Fig. 1. A leading-in conductor or electrode support is designated by the reference character 3|. For bringing out such a conductor from the envelope in an insulating manner, the container or header 30 is rst provided with an opening 32 large enough to provide a suflicient space about the conductor 3|. Secured to the member 30 as by welding, there is a cylinder 33, made of iron or nickel and having an outwardly extending ilange 34 on one end and an inwardly extending flange 35 on the other end. This cylinder is also provided with a relatively large opening 36 through which the conductor passes. Resting on the cylinder 33 and secured thereto as by welding, there is a heavy metal washer 31 which is preferably constituted of a special alloy. A cylinder of glass 38 is butt-sealed to the upper surface of the washer and is also sealed at its upper end to a cap member 39 provided with a flange for sealing purposes. terior surface of the cap member, which carries on its exterior surface a rod 40 to serve as a terminal for the rod 3i.

The rod 3| may be welded to the in- The cap member 39 and the heavy washer 31 iare preferably constituted of a metal which has substantially the same thermal expansion characteristic as the glass cylinder 38 at all temperatures from 0 C. up to and including the softening temperature of the glass. Examples of such materials are given hereinbefore.

A seal of this character may be made for various voltages by increasing or decreasing the length of the glass cylinder 3l. In addition, it is possible to utilize a metal for the cylinder 33 which may be more easily drawn and is less expensive than the metal of which washer 31 is composed. 'I'hus a seal of this type may be cheaply fabricated and the minimum amount of alloy having the proper thermal expansion characteristic required, yet an effective seal is obtained for bringing out conductors of all sizes, large and small, from the interior of the metal container to the exterior thereof.

In Fig. 3, the seal is somewhat similar to that shown in Fig. 2 so that corresponding elements have been given the same reference characters, except that the glass cylinder 38 is not buttsealed to the flanged cylinder 4i constituted of the special alloy. The cylinder 4I may be made of stock drawn to shape and utilizing the minimum quantity of alloy. This cylinder is preferably welded or otherwise secured to the heavy washer 42 which may be constituted of an inexpensive metal and which in turn is welded or otherwise secured to the member 30, which forms part of the metal envelope. Heavy washer 42 prevents transmission of strainsfrom member 30 to member 4I and the result is a saving in the amount of special alloy required for member 4I.

Fig. 4 shows a still different form of seal for carrying a combined leading-in conductor and support wire 3| through a portion 30 of a metal container in an insulating manner. Secured to the member 3|) there is a flanged cylindrical member 43. This cylinder contains a cylinder 44, to which it is welded. leaving an annular space therebetween for receiving one end of the glass cylinder 45. The cylinder 45 is sealed to each metal cylinder. The upper end of the glass cylinder -45 is sealed. on the interior, to a metal cylinder 46', while to the exterior surface of the glass cylinder there is sealed a metal cap member 41. The support, rod 3l is welded to the cap member and, if desired, an additional rod 4lmay be welded to the upper side of the cap member.

The cylinders 43, 44, 46, and." are preferably constituted of a special alloy having substantially the same thermal expansion characteristic as the glass cylinder 45 over the ertire temperature range between 0 C. and the softening temperature of the glass. The seal shown in Fig. 4 offers some advantages over those illustrated in Figs. 2 and 3 in that the glass cylinder is not butt-sealed to the metal member, but instead, a joint is formed between contiguous peripheral surfaces of the joined cylindrical members. 'Ihus larger insulating surfaces are offered between the metal and glass which provides greater mechanical strength and also greater resistance to leaks along the glass and metal boundary.

As in the case of the seals shown in Fig. 1, the seals illustrated in Figs. 2, 3, and 4 may be made by automatic machinery, on a quantity production basis, complete in themselves and apart from the metal header or other metal portion of the envelope. The seals may be readily secured to the envelope. By separating the operations of the seal as much as possible from the operations performed on the metal envelope, as for example, assembling and securing the screen grids 6 and the control grid I within the envelope, it is apparent that work on the tube as a whole can progress much faster than if the fabrication of the seals were intimately tied up with operations on the envelope. Furthermore, when the seals are formed separate from the' envelope in the manner described hereinbefore, any damage to the seals during fabrication causes the scrapping only of the seal in question and does not involve the remainder of the tube.

It is apparent that while we have described the various seals as being assembled and fabricated apart from the envelope, thereafter secured thereto, it will be understood that if desired, the

What we claim as new and desire to secure byl Letters Patent of the United States is:

1. An electric discharge device comprising a metal envelope and containing an electrode, means for supporting the electrode from the envelope, said means including a metal cylinder surrounding a support member for said electrode, and insulating material hermetically closing the clear space between the cylinder and the support member, said material having a length which is substantially less than the length of said cylinder and being positioned intermediate the ends of said cylinder, leaving a space of substantial dimension between each end of the material and the end of the cylinder.

2. An electric discharge device comprising a metal envelope and containing an electrode, means for supporting the electrode from the envelope, said means including a metal cylinder surrounding a support member for saidelectrode, said cylinder being provided with a flange which is secured to the envelope by a fused metal joint, and insulating material filling a portion of the space between the cylinder and the support member, said material being positioned entirely remote from said flange and leaving a clear space of substantial dimension between the material and the flange.

3. An electric discharge device comprising a metal envelope containing an electrode, said envelope comprising cylindrical and header members secured together, a metal eyelet secured to said header member by means of a fused metal joint, a leading-in conductor for said electrode, said conductor passing through said eyelet, and a body of glass between said conductor and said f eyelet, said glass being positioned remote from the joint between the eyelet and header member. 4. An electric discharge device comprising a sealed envelope, a metal header having an aperture therein and forming a portion of the wall of said envelope, and means for hermetically sealing a leading-in conductor through said header, said means comprising a flanged metal eyelet secured to said header by Joining its flange to the header in the region surrounding said aperture, and a body of glass sealing the conductor within said eyelet at a position remote from the flanged end of the eyelet.

THOMAS A. ELDER. ALBERT C. GABLE. 

